Gear compressors and expanders



United States Patent 3,531,227 GEAR COMPRESSORS AND EXPANDERS Roger C. Weatherston, Williamsville, N.Y., assignor to Cornell Aeronautical Laboratory, Inc., Buffalo, N.Y., a corporation of New York Filed July 5, 1968, Ser. No. 742,890 Int. Cl. F04c 17/04, 29/04 U.S. Cl. 418-94 6 Claims ABSTRACT OF THE DISCLOSURE A gear compressor apparatus having mating gear elements having spaced lobes, with a network of internal cooling passages and a low pressure uid inlet and a high pressure fluid outlet and feedback passages providing communication between the outlet and the space between the lobes of the gear elements before the lobes are exposed to the outlet.

A gear expander apparatus having mating gear elements having spaced lobes and a high pressure inlet and a low pressure outlet and passages associated with the space between each of the lobes of the gear elements providing communication with the outlet before the gear elements are exposed to the outlet.

BACKGROUND OF THE INVENTION The present invention relates to compressors and expanders, and, more particularly to an improved gear-type apparatus that can operate either as a compressor or expander.

Presently known gear pumps or compressors cannot operate in an efficient or practical manner when handling high temperature working uids, in excess of 2000 F., for example. At these high temperature conditions the leakage losses between the rotating gears and the lixed casing members and between the mating portions of the gears themselves are much higher than under more conventional, low temperature operation. This inability to operate satisfactorily is primarily due to the higher speed of sound and the higher leakage ow rates existing at such elevated temperatures.

In addition, conventional gear pumps or compressors do not precompress the inlet or low pressure gas before exposing it to the high pressure discharge side of the compressor. Hence, the prime mover for the compessor must provide all of the flow work required to deliver the entire volume ow of the inlet gas against the discharge pressure.

To reduce the leakage flow rate of conventional gear pumps or compressors, it would be desirable to drive the gear elements at high speed. However, when the pitch line velocityexceeds about one-tenth the speed of sound of the inlet gas, adverse momentum losses become significant. These losses are brought about by the sudden exposure of the gear wells, which are filled with low pressure inlet gas, to the high pressure outlet region 4bringing about a violent rush of high pressure gas back into the oncoming gear well. The direction of the rush of gas is against the motion of the gear, thereby creating adverse momentum forces which impede the gears movement, and decrease the efficiency of the compressor. Also, the operating noise of the compressor increases, rendering it less desirable to industry. t

SUMMARY OF THE INVENTION The foregoing, and other, disadvantages of the prior art are overcome according to the present invention, which provides, according to one aspect thereof, feedback passage means from the outlet high pressure region to the gear wells before they are exposed to the outlet region and oriented such that the gas flowing therethrough enters the well in a direction that is in harmony with the direction of gear motion. In this manner, momentum forces arise which are supplementary to the gear drive and consequently reduce the power input requirements, resulting in increased eficiency.

According to a second aspect of the present invention, internal cooling means are provided for the gear members, which, combined with certain optimum relationships between the horsepower, size, and speed of the gear compressor enable it to operate in temperature regimes heretofore thought impossible for a gear compressor.

BRIEF DESCRIPTION OF THE DRAWINGS For a more fuller understanding of the present invention, reference should now be made to the accompanying detailed description of the same taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of the improved gear compressor according to the present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. l;

FIG. 3 is a cross-sectional view of the basic gear compressor mechanism as modified to operate as an expander;

FIG. 4 is a partial sectional View taken along line 4-4 of FIG. 3; and

FIG. 5 is a sectional view taken along line 5 5 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and, more particularly, to FIGS, l and 2, the gear compressor according to the present invention is illustrated in section and depicted generally by the numeral 10. As shown the apparatus comprises upper and lower casings 12 and 14, respectively; having opposed flanges that are `bolted together at 16 defining a housing having various interior chamber regions, to be referred to hereinbelow. A suitable annular seal 18 may be provided to make the connection leak tight. The interior chambers dened by casing sections 12 and 14 have a pair of inlets 20 communicating with a low pressure region 21 thereof and an outlet passage 22 leading to a point of use from an interior high pressure region 24 thereof.

A pair of cylindrical gear members 26 and 28 are rotatably mounted inside the casing sections by suitable shafts and bearings 30 and 32, respectively. The gear members have a generally conventional exterior construction each providing alternately spaces lobes 33 that have front side faces 34 that face in the direction of motion of the gear and rear side faces 35 that face against the motion of the gears and wells 36. The wells and lobes of each gear coact in substantial meshing engagement as the gears rotate in the direction of arrows A and B.

Each of the gears 26, 2'8 is provided with internal cooling structure in the form of a coolant supply duct 38 extending axially through shaft 30 and through each of the gears, terminating short of the side ends thereof. Interiorly of each gear and adjacent the lobes 33 are a plurality of axial or longitudinal coolant passages 40 that communicate at one end with the coolant supply duct 38 by means of a plurality of radial branch passages 42. The other end of passage 40 communicates with a plurality of radial coolant return passages 44 each of which lead to an annular axial or longitudinal duct 46 passing through the gear and shaft to a suitable reservoir (not shown).

Means to separate the gear wells from direct communication with said inlet or outlet region as the gears rotate is provided in the form of a pair of opposed projecting ledges `48 and 5t) that extend into high pressure outlet region 24 and having curved undersurfaces 52 and 54 that are contoured to envelop the gear wells and seal against the periphery of each of the lobes 33. Each ledge has feedback passage means for providing restricted communication between the outlet high pressure region 24 and each of the gear wells in a sequential manner before the wells are fully exposed to the high pressure region. In addition, the feedback means is so oriented with respect to the rotational direction of each gear such that the high pressure outlet fluid from region 24 feeds each of the gear wells 36 in such a manner to impart a force to the adjacent lobe in the same direction as the gear is rotating.

Thus, as shown in FIG. l the feedback means may comprise one or more passages 56 extending through the ledges 48, 50 from a top surface thereof to the bottom surface 52, 54 that are inclined generally downwardly and inwardly toward the center of the apparatus to direct the fluid stream passing therethrough against the rear side face 35 of the lobe 34 whereby a momentum force is developed against the side face that augments the torque imparted t the gears by its external driving means (not shown). Although as illustrated the feedback passage 56 communicates with only one well 36 of each gear at one time, it is contemplated by the present invention that additional feedback passages may be provided that would simultaneously feed more than one well. Alternatively, passages can be placed between the wells such that feedback fluid flows through one well and then sequentially through the others. It is also possible to have the feedback passages external of the housing whereby the feedback flow that fills the gear wells may be cooled before entering them to promote a cooler operating machine.

In the operation of the embodiment of FIGS. l and 2, low pressure inlet gas flows through passages into the gear wells 36 from which it is ultimately compressed by the action of the opposed meshing lobes (as is well known) and discharged into the high pressure outlet region 24. A portion of the high pressure outlet gas is fed back into the well 36 of each gear via passages 56. As pointed out, supra, the jet of outlet uid from passage 56 acts on the rear face 35 of the gear lobes applying an additional force which acts inthe direction of motion of each gear to augment the input shaft work and thereby increase the efficiency of the compressor. Without the provision of passage 56, the sudden rush of high pressure outlet iiuid into the low pressure well as soon as the same is slightly cracked to the outlet region, would create an impulse or momentum force on the front face 34 of the lobe, the direction of which would be against the motion of the gears, resulting in a decrease in compressor efficiency.

The feedback line 56 has the additional advantage of smoothing out pulsations and noise of the apparatus. This is accomplished by sizing the line 56 to set the rate of feedback flow into the wells such that the filling process takes longer than would be experienced in the conventional deign. In this manner the gear wells are virtually filled to the discharge pressure level by the time they become exposed to the outlet region; this being true regardless of the orientation of the feedback passage.

It has been found that the internal gear cooling structure described above combined with minimum power levels of approximately 500 horsepower, pitch line velocities in excess of feet per second and a lobe side face area of at least l0 square inches will allow the compressor to operate satisfactorily at temperatures in excess of 2000 F. At these minimum conditions it has been determined that the leakage loss would be 0.145 of the input flow. In contrast, calculations for conventional compressors indicate intolerable leakage losses at high temperatures when driven at conventional speeds of about 100 feet per second.

FIGS. 3, 4 and 5 depict a second embodiment wherein the basic mechanism is modified to function as an expander. In these figures, like numerals primed refer to like numeral parts of the FIG. 1 embodiment.

Referring now to FIGS. 3, 4 and 5, the apparatus 10 CII has an outlet passage 20 communicating with the outlet region 21 and the interior of casing sections 12 and 14 and a high pressure inlet passage 22 communicating with an interior high pressure region 24. Gears 26' and 28' are provided which are generally similar to the gears 26 and 28 of the previous embodiment having lobes 33 and wells 36. The lobes have rear side faces 34 and front side faces 35 and the direction of rotation of each gear is now indicated by arrows C and D.

Fixedly attached, as by pin 60, to opposite ends of each gear 26 and 28 is a cylindrical plate 62, the diameter of which being substantially equal to the lobe diameter of the gears. The plate 62 provides a closure for one end of the gear well channel, whereas casing 12 provides a closure for the other end, as clearly shown in FIG. 5. Plate 62 has a plurality of inclined passages 64 that communicate at one end with the gear wells 34 and at the other end with the edge surface 66 of the plate. As shown in FIG. 3, the passages 64 are inclined such that the axis thereof is substantially perpendicular to the rear side faces 34 of the lobes 33.

In this embodiment the leges have hollow interiors in communication with outlet passage 20', and lower curved portions 54 that envelop peripheral surface portions of the gear members and the portions of the surface edge of plate 66, except for a cutaway or recess slot 55 directly above plate 66 and of substantially the same width, as shown in FIG. 4. It thus can be seen that communication is established by way of passage 64 and recesses 55 between each of the gear wells prior to the exposure thereof directly to the outlet region 21 when they rotate beyond the surface 54.

In the operation of the FIG. 3 embodiment, high pressure driving fluid enters region 24 and acts on the lobes causing them to rotate inthe direction of arrows C and D as is well known. During rotation, each well 36 is filled with high pressure gas, some of which is exhausted to the low pressure region 21 through passage 64 as the wells rotate in the vicinity of recess 55. Due to the fact that the axis of passage 64 is substantially perpendicular to the rear face 34 of each lobe, the expulsion of high pressure gas therethrough creates a reaction force which acts in the direction of motion of this face and therefore functions to augment the work imparted to the gears by the expanding gases. Thus, the output work is increased, which increases the eiciency of the expander.

Without the provision of passages 64, after each well is filled from the high pressure region 24', the wells rotate under surface 54 and eventually become exposed to the low pressure region 21. As each gear well becomes exposed, the high pressure gas that is trapped therein would be expelled in a direction that is generally opposite to the front face 35 of the lobes, thereby creating a reaction force against this front face, which acts opposite to the direction of motion of the gears. This results in torques acting against the output torque of the expander to thereby decrease its efiiciency. With the present invention, such decrease in eiciency is eliminated, because by the time the gear well is exposed directly to the outlet region, the pressure therein is virtually equal to the outlet pressure.

Although the foregoing has described preferred embodiments, according to the present invention other variations will occur to those skilled in the art. For example7 a compressor with two or three lobes may be-utilized. It is therefore intended that the present invention bc limited only by the scope of the appended claims.

I claim:

1. The apparatus of the character described, comprismg;

(a) a housing,

(b) a pair of cooperating gear members rotatably mounted in said housing,

(c) alternately spaced lobes on said gear members,

having a front side face that faces in the direction of motion of said gears and a rear side face that faces against the direction of motion of said gears,

(d) gear wells between said lobes,

(e) inlet passage means communicating with an inlet region of said housing,

(f) outlet passage means communicating with an outlet region of said housing, l

(g) means for separating portions of said gear wells from direct communication with said inlet and outlet region as said gears rotate,

(h) means providing restricted communication between said outlet region and said gear wells before said gear wells become directly exposed to said outlet region,

(i) said last mentioned means comprises passages at least some portions of which have an axis that is substantially perpendicular to each of said rear side faces of said lobes when said passages are in communication with said wells, and

(j) said passages are carried by said gears to rotate therewith.

2. The apparatus according to claim 1, further compris- (Ik) plates iixedly attached to opposite ends of said gears providing a closure for one end of each of said wells, and

(l) said passages are located in said plates.

3. The apparatus according to claim 2, wherein;

(m) said means for separating comprises a hollow ledge projecting into said housing, the interior of which communicates with said outlet,

(n) said ledge has a lower curved surface that envelopes a peripheral portion of said gears, and

(o) a recess in said surface for communicating with said passages.

4. A gaseous uid compressor, comprising;

(a) a housing,

(b) a pair of cooperating gear members rotatably mounted in said housing,

(c) alternately spaced lobes on said gear members, having a front side face that faces in the direction of motion of said gears and a rear side face that faces against the direction of motion of said gears,

(d) gear wells between said lobes,

(e) inlet passage means for delivering low pressure gaseous fluid to an inlet region of said housing, (f) outlet passage means communicating with a high pressure gaseous outlet region of said housing,

(g) a pair of opposed projecting ledges extending into said high pressure outlet region, each of said ledges 50 having curved undersurfaces which envelop said gear wells and seal against the periphery of said lobes, the extremeties of said ledges defining an opening that provides communication between said high pressure outlet region and the volume that is bounded by said undersurfaces and the mating portions of said gears, and

(h) feedback passage means in each of said ledges,

spaced from said opening, for providing communication between said high pressure outlet region and said gear wells prior to the exposure thereof to said opening, said feedback passages being so constructed and arranged with respect to the direction of motion of said gears that the flow of high pressure uid therethrough into said wells is directed against the rear side face of said lobes, the size of said feedback passage means being so related to each gear well volume that each well substantially reaches the pressure existing in said high pressure outlet region as each gear well becomes exposed to said opening.

5. The apparatus according to claim 4, further providlng;

(j) coolant passage means internally of said gears for supplying a coolant iluid adjacent said lobes, wherein,

(k) said lobe faces each have an area of at least ten square inches and a pitch line velocity of at least 300 feet/sec., and

(l) said gears are driven by input power means in excess of 500E horsepower.

6. The compressor according to claim 4 wherein said feedback passage means extend from said high pressure outlet region through said ledges downwardly and inwardly toward the mating portion of said gears.

References Cited UNITED STATES PATENTS 1,252,160 1/1918 Pagel.

2,489,887 11/ 1949 Houghton 230-210 2,491,365 12/1949 Ernst.

2,624,287 l/ 1953 Ilyin.

2,781,730 2/ 1957 Newmier.

2,799,253 7/ 1957 Lindhagen et al. 23'0-210 2,801,792 8/ 1957 Lindhagen et al 230-.210 2,938,664 5/1960 Noller 230-210 3,204,564 9/ 1965 Eltze.

DONLEY I. STOCKING, Primary Examiner W. I. GOODLIN, Assistant IExaminer U.S. Cl. X.R. 418- 

